The present disclosure relates to an optical system support, especially for an optical measuring device, comprising a basic body on which means for fixing components of an electrooptical transceiver system are provided. Furthermore, the present disclosure relates to a production process for such an optical system support. In addition, the present disclosure relates to an optical measuring device, especially a laser rangefinder, comprising a lens holder, an optical system support and a transceiver system.
DE 10 2005 041 980 A1 discloses an optical measuring device for laser rangefinding which is designed as a handheld device. Provided as a central element in the laser rangefinder is an optical system support made of plastic, on which an electrooptical transceiver system is held. For this purpose, the optical system support has receptacles and fastening means for the optical and/or electronic components of the measuring device. For instance, a lens holder with a receptacle for a receiving optical system is provided integrally on the front region of the optical system support. Furthermore, a printed circuit board, with a laser diode with a collimator lens mounted in front of it for producing a laser beam and a light-sensitive receiving diode, is held on the optical system support. The printed circuit board is positioned in the measuring device in such a way that the laser diode can emit the light beam through the transmitting optical system and the light-sensitive receiving diode is positioned at the focal point of the receiving optical system. To improve the measuring accuracy and to reduce measuring errors, the light paths for transmitting and receiving are arranged in parallel. As a result, external influences on the optical system support act on the two light paths equally.
The optical system support with the electrooptical transceiver system fixed thereto is mounted together with a display device, an input device and an energy supply device in a common housing. During operation, the laser rangefinder is actuated by way of the input device. Then, a laser beam is emitted from the laser diode onto an item from which the distance is to be measured. The point of light projected onto the item is concentrated on the light-sensitive receiving diode and evaluated by means of the receiving optical system. The distance value obtained by the measurement is output by way of the display device.
In practice, optical measuring devices have to meet high requirements for their mechanical load-bearing capacity. Already during assembly, forces that may lead to deformations may act on the optical system support. During use, the device may also be exposed to shocks and thus be deformed. This can only be compensated or prevented partly by structural design measures. For handheld optical measuring devices especially, there are limits to this on account of their functional purpose. For instance, steel is in fact a suitable material since it has a great modulus of elasticity (see Table 1). Diecast aluminum and cast magnesium are less suitable in this respect and plastic has the lowest modulus of elasticity. However, for reasons of weight, the use of steel is disadvantageous, since it is the heaviest of the materials listed in Table 1.
TABLE 1MaterialModulus of elasticitySteel (bent plate part, St 37)210000 N/mm2Diecast aluminum (GD-AlSi 12) 75000 N/mm2Cast magnesium (GD-MgAl5) 50000 N/mm2Plastic (PPS-GF40) 13000 N/mm2
Furthermore, the measuring devices are subjected to thermal influences, for example by solar irradiation. If the optical system support is fixedly connected to the housing, this may lead to bending if it is heated on one side, whereby the optical system support is deformed and the measuring accuracy is reduced. It is therefore desirable that the material has on the one hand a high thermal conductivity and on the other hand a low coefficient of thermal expansion. As can be seen from Table 2, this combination is the most suitable in the case of steel, while it is the least suitable in the case of plastic.
TABLE 2ThermalCoefficient ofMaterialconductivitythermal expansionSteel (bent plate part, St 37)48-58 W/mK13 μm/mKDiecast aluminum (GD-AlSi 12)160 W/mK21μm/mKCast magnesium (GD-MgAl5)200 W/mK26 μm/mKPlastic (PPS-GF40)0.3 W/mK20-40 μm/mK
Since the electrooptical transceiver system contains electronic components which, on account of the modulation frequencies that are used of up to 1 GHz, generate an electromagnetic radiation, requirements for electromagnetic compatibility must also be observed.
Although, in principle, the optical system support can serve as a shielding if it is produced from conducting material, this is difficult on account of the high modulation frequencies that are used. Therefore, the optical system support should be produced from a material with a low electrical conductivity, with the result that it cannot itself act as an antenna for the electrooptical transceiver system, and consequently does not contribute to the radiation. The metallic materials steel, diecast aluminum and cast magnesium all have a high conductivity, with the result that they are less suitable from the aspect of electromagnetic compatibility. Only plastic, as an insulator, is well suited for this.
TABLE 3MaterialElectrical conductivitySteel (bent plate part, St 37)about 10m/ohms mm2Diecast aluminum (GD-AlSi 12)19-22m/ohms mm2Cast magnesium (GD-MgAl5)8m/ohms mm2Plastic (PPS-GF40)insulated
In addition, the optical system supports produced by diecasting or injection diecasting have production-related internal stresses. This effect is also present in principle in the case of bent steel plate parts. These internal stresses relax during the lifetime and with temperature, so that over time there is a misalignment of the optical system.
Depending on the materials that are used, production-related accuracy limits are predetermined for the optical system support, and consequently for the optical measuring device. The production-related accuracy is lowest in the case of diecast aluminum and increases through cast magnesium and plastic to steel.
In the assembly of the optical measuring device, adhesive is often used, since adhesive bonding largely avoids stresses in the optical system support being caused by assembly and can be carried out with low costs and high accuracy. Cast metal materials are generally less suitable for this than steel or plastic, since they generally have poorer adhesive bonding properties. The use of adhesives is also restricted since, for example, metals are not transparent, with the result that it is not possible to use light-curing adhesive to carry out the adhesive bonding operation more quickly. Only plastics materials can be produced in a transparent form allowing a light-curing adhesive to be used.
Altogether, it can be stated that no material meets all the desired requirements. The most suitable materials appear to be steel or plastic, plastic being disadvantageous in particular with respect to its stability and thermal properties, whereas steel is critical in particular with regard to electromagnetic compatibility. In addition, the internal stress in particular must be regarded as disadvantageous in the case of all the materials previously used.
It is therefore an object of the present disclosure to provide an optical system support that has simultaneously a high mechanical and thermal load-bearing capacity, good electromagnetic compatibility, a long lifetime, can be produced with high accuracy and can be easily assembled.